1. Field of the invention
The present invention relates, in general, to a carbon molecular sieve material and, more particularly, to a carbon molecular sieve material with structural regularity, which is suitable for use in catalysts, adsorbents, carriers, sensors, and electrodes. Also, the present invention is concerned with a method for preparing such a carbon molecular sieve material. In addition, the present invention is directed to use of the carbon molecular sieve material.
2. Description of the Prior Art
Among porous materials, those having three-dimensionally arranged pores with uniform sizes, like zeolite, are defined as molecular sieves. Since the uniform pores make such molecular sieves be selective for specific sizes of molecules, they are extensively used as catalysts, catalyst supports, or adsorbents.
Compared with metal oxide type molecular sieves such as zeolite, carbon molecular sieves are found to have advantages in thermal stability, hydrothermal stability, chemical resistance and lipophilicity, and active research and development is directed to carbon molecular sieves.
Most of the carbon molecular sieves having been developed thus far are synthesized through the pyrolysis of natural vegetable materials such as coconut or synthetic polymers. Owing to higher sparsity of impurities such as metals or metal oxides, carbon molecular sieves are dominantly prepared from synthetic polymers. Such carbon molecular sieves are, for the most part, 0.5 nm or less in pore size. By controlling the thermal decomposition temperatures or by an after-treatment with oxygen, their pore sizes can be increased, but to a limited degree.
In the meanwhile, there has been made many efforts to synthesize carbon sieves by selectively adsorbing polymers or propylene gas onto active carbon and decomposing them. The resultant materials have relatively uniform distribution in pore size compared with the active carbon, so that they show properties of molecular sieves. However, because of the absence of regularity in their whole structures, the X-ray diffraction patterns of the above materials are close to those of amorphous carbons. In addition, the techniques suffer from disadvantages in that conditions for the adsorption and decomposition are quite stringent.
In adsorption and separation functions, conventional carbon molecular sieves having developed thus far are restrained to small molecules. For instance, they have been used as adsorbents for storing small molecules such as hydrogen and methane or to separate nitrogen or oxygen from the air.
Recently, a group of researchers at Mobil Co. reported a series of mesoporous molecular sieves, named the M41S series, including MCM-41 and MCM-48 as disclosed in U.S. Pat. Nos. 5,057,296 and 5,102,643. Since then, various mesoporous molecular sieves, such as SBA-1, SBA-15, KIT-1 and MSU-1, have been developed.
Ranging, in pore size, from 2 to 30 nm, mesoporous molecular sieves are synthesized through a liquid crystal template pathway by using surfactants as templates. These mesoporous molecular sieves have advantages in that their pore sizes can be adjusted in a range of 1.6 to 30 nm by controlling the kinds of surfactants or synthetic conditions employed during the production process. Further, they can be synthesized to have various structures by virtue of the versatility of the templates. In past, research was made on template techniques in which various organic materials were filled within the pores of zeolite and thermally decomposed, followed by removing the silica framework to produce carbon molecular sieves. However, such techniques are found to fail because, when the template zeolite is removed, the carbon structure does not stand by itself, but collapses.
Leading to the present invention, the intensive and thorough research on carbon molecular sieves, repeated by the present inventors aiming to overcome the above problems encountered in prior arts, resulted in the finding that specific inorganic mesoporous molecular sieves are useful as templates from which carbon molecular sieves can be synthesized with uniform pore sizes and structural regularity. Using a carbonization method of the present invention, there can be obtained carbon molecular sieves in which pores with uniform diameters are regularly arranged. Such materials with regularity can find numerous applications in catalyst supports, organic adsorbents, sensors, electrodes, etc.
Therefore, it is an object of the present invention to provide a method for preparing structurally regular carbon molecular sieves in which pores with uniform diameters are three-dimensionally arranged.
It is another object of the present invention to provide carbon molecular sieves with structural regularity.
It is another object of the present invention to provide use of the structurally regular carbon molecular sieves.
In accordance with the present invention, there is provided a method for preparing a carbon molecular sieve material comprising the steps of: adsorbing a mixture of an aqueous carbohydrate solution and an acid or a polymer precursor into pores of an inorganic molecular sieve material; drying and polymerizing the adsorbates; re-adsorbing a mixture of an aqueous carbohydrate solution and an acid or a polymer precursor onto the resultant mixture obtained in the previous steps, and drying and polymerizing the adsorbates; carbonizing the adsorbates through thermal decomposition; and removing the framework of the inorganic molecular sieve from the carbonized adsorbates by use of a hydrofluoric acid or a sodium hydroxide solution.